1. Field of the Invention
The present invention relates to an electroacoustic transducer comprising a multifaced diaphragm assembly that includes a diaphragm obtained by combining a plurality of polygonal diaphragm segments into a nearly spherical shell shape, and a plurality of speaker driving units arranged inside the multifaced diaphragm assembly so that each speaker driving unit opposes the corresponding diaphragm segment.
2. Description of the Related Art
An electroacoustic transducer (speaker) for producing sound from an audio signal is realized in various forms, one of which is for example a point-source omnidirectional speaker system that delivers reproduced sound to human ears as if the sound is radiated from a pulsating sphere (refer to, for example, Japanese Patent Application Laid-open Publication No. 1309-70092).
The aforementioned pulsating sphere is a sound source considered as an ideal form of an omnidirectional speaker. This sound source produces the same sound pressure in all directions as if a balloon vibrated by expanding and shrinking itself, thereby radiating sound completely omnidirectionally. The name of pulsating sphere is given to such a sound source because the sphere vibrates as if pulsating.
FIG. 1 is a perspective view of an example of a related art point-source omnidirectional speaker system. FIG. 2 is a block diagram of the related art point-source omnidirectional speaker system. FIG. 3 is a frequency response of a speaker unit constituting the related art point-source omnidirectional speaker system, in which peaks and dips in the frequency response is representatively shown.
A point-source omnidirectional speaker system 100 shown in FIGS. 1 and 2 is one disclosed in the above publication (Japanese Patent Application Laid-open Publication No. H09-70092), which will be briefly outlined referring thereto.
As shown in FIG. 1, in the related art point-source omnidirectional speaker system 100, a hollow spherical enclosure 101 with rigidity is configured into a polyhedron having a total of 32 faces consisting of 12 pentagonal first faces 101a and 20 hexagonal second faces 101b. By the way, the enclosure 101 is also called a speaker cabinet or a speaker box.
On each of the first faces 101a and the second faces 101b of the enclosure 101, there is provided a full-range speaker unit 102 as exemplified in FIG. 1.
In addition to the above example, there is disclosed another example where a low-pitched sound speaker unit 103 is provided on each of the first faces 101a of the enclosure 102 and a high-pitched sound speaker unit 104 is provided on each of the second faces 101b. 
Moreover, FIG. 2 shows that a digital input signal 110 is supplied to the speaker units 102 (or 103 and 104) through a digital signal processor (DSP) 111 accompanying an operation panel 112, a digital-to-analog (D/A) converter 113, an analog attenuator 114, and a power amplifier 115 in this order.
When a speaker assembly in which the full-range speaker units 102 (or the low-pitched sound speaker units 103 and the high-pitched sound speaker units 104) are arranged on the enclosure 101 of a polyhedron having 32 faces (truncated icosahedron) is driven to radiate sound, peaks P and dips D appear in its frequency response as representatively shown in FIG. 3. In order to reduce the peaks P and the dips D, a drive signal that drives each speaker unit 102 (or 103, 104) is processed by filtering in the DSP 111 shown in FIG. 2, the filtering having a compensatory characteristic to the dips D, and then the processed drive signal is converted to an analog signal by the D/A converter 113. Then the analog signal is supplied to the speaker unit 102 (or 103, 104) after passing through the analog attenuator 114 and the power amplifier 115 in this order. This is what is disclosed in the above publication.
By the way, although the related art point-source omnidirectional speaker system 100 mentioned above has the full-range speaker units 102 (or the high-pitched sound speaker units 103 and the low-pitched sound speaker units 104) arranged on the enclosure 101 having a shape of truncated icosahedron, a portion that vibrates to produce sound is apparently limited to a specific diaphragm (not shown) that is integrated to each speaker unit 102 (or 103 and 104).
In such a configuration, there exists no vibratory portion between the neighboring speaker units but a rigid portion that constitutes apart of the enclosure 101, so that synthetic sound produced by mixing of sound from each speaker unit 102 (or 103 and 104) may not emulate sound from a point source.
In addition, while the dips D appearing in the frequency response of the sound produced by each speaker unit 102 (or 103 and 104) is reduced due to a compensatory filtering performed by the DSP 111, as explained with reference to FIG. 3, such filtering can be unnecessitated if the configuration of the speaker unit per se is able to reduce generation of the dips D.
Therefore, there has been awaited an electroacoustic transducer that can provide an omnidirectional point source of sound as a pulsating sphere and reduce the dips appearing in the frequency response of the sound produced by a plurality of speaker units. In addition, there has been desired an electricacoustic transducer that can be productively assembled into a three dimensionally radial shape, even when the transducer has to be assembled in a way that a multifaced diaphragm assembly having a shape of a nearly spherical shell is created so as to include a diaphragm obtained by combining a plurality of polygonal diaphragm segments and then a plurality of speaker drive units are arranged inside the multifaced diaphragm assembly so as to respectively oppose the corresponding diaphragm segment.